High-Energy Density Nancomposite Capacitor

ABSTRACT

A composite film having a high dielectric permittivity engineered particles dispersed in a high breakdown strength polymer material to achieve high energy density.

The present invention claims priority on U.S. Provisional PatentApplication Ser. No. 62/243,394 filed Oct. 19, 2015, which isincorporated herein by reference.

This invention was made with U.S. government support under Contract No.W15QKN-13-C-0070 awarded by Department of Defense Small BusinessInnovation Research (SBIR). The U.S. government has certain rights inthe invention.

The invention relates in general to high energy density nanocompositecapacitors that include nanoceramic filler in a polymer material. Moreparticularly, the invention relates to a nanocomposite having a highdielectric permittivity nanoengineered particles dispersed into a highbreakdown strength polymer material to achieve high energy density. Theceramic fillers are designed as core-shell structure, followed bycoating the second layer of functional groups, to achieve a gooddispersion in the polymer material and without causing a significationreduction in breakdown strength, leading to high-energy density.

BACKGROUND OF THE INVENTION

High-energy density capacitors play a critical role in numerous militaryand commercial pulsed power applications; however, the currentstate-of-the-art technology suffers from low-energy density, making thembulky and costly. Deployment of current and future pulse power devicessuch as radar devices, lasers, rail guns, high-power microwaves,defibrillators and pacemakers, will continue to rely on the developmentof high-energy density capacitors.

Current pulse power devices often use polymer film capacitors, whichinclude biaxially oriented polypropylene (BOPP), polyethyleneterephthalate (PET), polystyrene (PS), polycarbonate (PC) and polyimide(PI), all of which have the advantage of high dielectric breakdownstrength. However, all the mentioned polymers have low dielectricpermittivity (2-3.2), which highly limits the energy density of thecapacitor. For example, the current state-of-the-art active filmmaterial for capacitors is BOPP, which offers a capacitor energy densityof 1.2 J/cc, but is restricted by its low dielectric permittivity, thuslimiting the size and cost of these systems.

The current challenge of pulse power devices is obtaining high energydensity. Theoretically, the energy density is linearly proportional tothe dielectric constant and quadratically related to the breakdownstrength of the capacitor. Therefore, many efforts have been devoted toenhance the material's permittivity and/or breakdown strength to improvethe energy density. Currently, commercial monolithic materials arereaching a plateau in terms of energy density, due to the trade-offbetween the dielectric permittivity and breakdown strength of thematerials. Nanocomposites combining a high breakdown strength polymerand a high dielectric permittivity ceramic filler offer significantpromise for future high-energy density capacitors. While currentnanocomposites improve the dielectric permittivity of the capacitor, thegains come at the expense of the breakdown strength, which limits theultimate performance of the capacitor. Therefore, there is an increaseddemand to capture high dielectric permittivity from ceramic and highbreakdown strength from polymer to achieve high energy density.

BRIEF SUMMARY OF THE INVENTION

The present invention relates in general to high-energy densitynanocomposite capacitors that include nanoceramic filler in a polymermaterial. The invention also relates to a nanocomposite having a highdielectric permittivity nanoengineered particle dispersed in a highbreakdown strength polymer material to achieve high-energy density. Thepresent invention addresses these needs by creating a gradient interfacebetween the fillers and material to attain a high permittivity whilemaintaining a high breakdown strength leading to high-energy density.One non-limiting application of the invention is for use in pulse powerdevices, such as radar devices, lasers, rail guns, high-power microwavedevices, defibrillators, and pacemakers; however, the invention can beused in other devices or components such as inverters, converters,motors, DC bus capacitors, high-power lighting and others.

In one non-limiting aspect of the invention, the invention is directedto a novel method to prepare ceramic fillers that are calcined orinclude components that are calcines at different temperatures to adjusttheir structure and particle size. By incorporating the ceramic fillerswith different structure and particle size into a polymer, the energystorage performance of the composite can be tuned. High dielectricpermittivity nano-ceramic fillers can then be coated into a thin layerof insulator films into a core-shell structure to increase breakdownstrength. Furthermore, the invention relates to the coating of thecore-shell structure particle with a second layer of functional groupsto create a gradient interface. This engineering process makes thenanoparticles well dispersed into a high breakdown strength polymermaterial providing an improved breakdown strength in the nanocomposite.The composites can optionally be formed as a solution casting of polymersolution into nanocomposite films. The whole process can optionally beformed as a pilot scale to produce nanocomposite films. Thenanocomposite films can optionally be fabricated into capacitors usingcommon industry methods and equipment. The invention also relates to theuse of the nanocomposite capacitor acting as a key energy source andcomponent for pulse power devices and energy storage devices, such as,but not limited to, radar devices, lasers, rail guns, high-powermicrowaves, defibrillators and pacemaker deployment; however, theinvention can be used in other devices or components such as inverters,converters, motors, DC bus capacitors, high power lighting and others.

In another non-limiting aspect of the invention, there is provided a newand improved nanoceramic powder for high-energy density nanocompositecapacitor fabrication. The novel nanoceramic powder can be doped andcalcined at different temperatures to achieve high dielectricpermittivity nanocomposites. This invention also is directed to acalcining process to achieve the goal of high energy densitynanocomposite capacitors. By incorporating the ceramic fillers (calcinedat different temperature) into the polymer, the energy storageperformance of the composite can be adjusted.

In still another non-limiting aspect of the invention, there is provideda method for engineering nanoparticles to create a gradient interfacebetween the filler and the polymer material to increase breakdownstrength of the nanocomposite. The functionalized nanoparticles aregenerally well dispersed in the polymer material. One non-limitingfabrication method in accordance with the present invention includes thesteps of 1) coating a thin layer of high dielectric strength material onthe ceramic with core-shell structure, and 2) modifying the core-shellstructure particle with functional groups. This hierarchical structurecreates a gradient interface between the particle and polymer material,improves the dispersion of the particles, and improves breakdownstrength of the nanocomposites.

In yet another non-limiting aspect of this invention, there is provideda combined high dielectric permittivity filler and gradient interface.As used herein, ‘high-energy density capacitor’ generally means greaterthan about 3 J/cc. Such high-energy density nanocomposite capacitors canbe used for pulse power devices, such as rail guns, lasers, radardevices, defibrillators and pacemaker deployment; however, the inventioncan be used in other devices or components such as inverters,converters, motors, DC bus capacitors, high-power lighting and others.

In summary, the present invention is composite film, a method forforming a composite film, and devices or components that include thecomposite film. The composite film includes a polymer material thatincludes a plurality of particles of high dielectric permittivityceramic filler. The high dielectric permittivity ceramic filler has acore-shell structure. The core of the core-shell structure has adifferent composition than the shell of the core-shell structure. Theouter surface of the particles of the high dielectric permittivityceramic filler is modified with one or more functional groups. Thecomposite film can be formed by 1) forming a plurality of particles ofhigh dielectric permittivity ceramic filler, wherein the high dielectricpermittivity ceramic filler has a core-shell structure, and a core ofsaid core-shell structure has a different composition than a shell ofsaid core-shell structure; 2) modifying an outer surface of theplurality of particles of the high dielectric permittivity ceramicfiller with one or more functional groups; dispersing a plurality of themodified particles of the high dielectric permittivity ceramic fillerinto a polymer material; and 3) solution casting the polymer materialhaving the plurality of the modified particles of the high dielectricpermittivity ceramic filler into a film to form the composite film. Inone non-limiting embodiment, the polymer material can optionally includepolar groups. In another and/or alternative non-limiting embodiment, theshell is formed of a dielectric material that has at least three times(e.g., 3-1000 times and all values and ranges therebetween) thebreakdown strength of the material used to form the core. In anotherand/or alternative non-limiting embodiment, the high dielectricpermittivity ceramic filler has a particle size of less than 1 micron,generally, has a particle size of about 10 nanometer to less than about1 μm (and all values and ranges therebetween), more typically has aparticle size of about 10-500 nanometers, still more typically has aparticle size of about 20-450 nanometers, and even more typically has aparticle size of less than about 100 nanometers. In another and/oralternative non-limiting embodiment, the shell has a coating thicknessof at least about 10 Å and less than 1 μm (and all values and rangestherebetween), and typically the shell has a coating thickness of lessthan 100 nanometer, and more typically the shell has a coating thicknessof less than 10 nanometer. In another and/or alternative non-limitingembodiment, the core of the high dielectric permittivity ceramic fillerincludes a high dielectric material, the shell includes a high breakdownstrength material, the core is at least partially encapsulated by theshell and is typically fully encapsulated by the shell. In anotherand/or alternative non-limiting embodiment, the high dielectric materialincludes one or more materials selected from the group consisting ofBaTiO₃, (Pb(Zr_(x)Ti_(1-x))O₃), Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃,CaCu₃Ti₄O₁₂, TiO₂, BaSrTiO₃, and Ba_(0.8)Pb_(0.2)(Zr_(0.12)Ti_(0.88))O₃.In another and/or alternative non-limiting embodiment, the shellincludes one or more materials selected from the group consisting ofAl₂O₃, SiO₂, Si₃N₄, MgO, aluminosilicates, mica, and diamond. In anotherand/or alternative non-limiting embodiment, the high dielectric materialincludes BaTiO₃ and the shell includes Al₂O₃ and, MgO and/or SiO₂. Inanother and/or alternative non-limiting embodiment, the thickness of theshell is less than the particle size of the core. In another and/oralternative non-limiting embodiment, the composite film has a greaterdielectric constant than a dielectric constant of the polymer materialand any polymer included in the polymer material that is used to formthe composite film. In another and/or alternative non-limitingembodiment, the composite film has a greater breakdown strength than abreakdown strength of any of the high dielectric permittivity ceramicfiller in the composite film. In another and/or alternative non-limitingembodiment, the high dielectric permittivity ceramic filler in thecomposite film has one or more properties selected from the groupconsisting of a) a plurality of different particle sizes of the highdielectric permittivity ceramic filler, b) the high dielectricpermittivity ceramic filler is formed of particles that have beencalcined at different temperatures, c) the high dielectric permittivityceramic filler is formed of particles formed of different materials. Inanother and/or alternative non-limiting embodiment, dielectricperformance, dielectric permeability, energy storage performance, andcombinations thereof of the composite film is achieved by adjusting acrystal structure, a particle size, or combinations thereof of the highdielectric permittivity ceramic filler. In another and/or alternativenon-limiting embodiment, the adjusting of the crystal structure,particle size, or combinations thereof of the high dielectricpermittivity ceramic filler is achieved by a) calcining a plurality ofthe high dielectric permittivity ceramic filler at differenttemperatures for inclusion in the polymer material, b) incorporatingdifferent composition high dielectric permittivity ceramic filler in thepolymer material, and/or c) incorporating a plurality of differentparticle sizes of the high dielectric permittivity ceramic filler insaid polymer material. In another and/or alternative non-limitingembodiment, the polymer material includes one or more compounds selectedfrom the group consisting of polyvinylidene fluoride (PVDF), PVDFcopolymers such as trifluoroethylene (P(VDF-TrFE)), hexafluoropropylene(P(VDF-HFP)) and chlorotrifluoroethylene (P(VDF-CTFE)) as well asterpolymers such as poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)),polytetrafluoroethylene (PTFE), polyimide (PI), Teflon™, polyethylenenaphthalate (PEN), polypropylene (PP), polycarbonate (PC), polystyrene(PS), polyphenylene sulfide (PPS), polyether ether ketone (PEEK),polyethylenimine (PEI), and polyarylsulfones (PSU). In another and/oralternative non-limiting embodiment, the one or more functional groupsbonded to an outer surface of the particles of the high dielectricpermittivity ceramic filler includes one or more compounds selected fromthe group consisting of an amine group, a hydroxyl group, a phosphonategroup, a silyl group, and a carboxylic group. The thickness of the layerof the one or more function groups is at least 1 Å, typically 1 Å to 500nm (and all values and ranges therebetween), and more typically 3 Å to80 nm. Generally, the thickness of the layer of the one or more functiongroups is less than the thickness of the shell.

In another and/or alternative non-limiting embodiment, one or more ofthe particles of the high dielectric permittivity ceramic filler in thepolymer material has a greater relative permittivity than the polymermaterial. In another and/or alternative non-limiting embodiment, all ofthe particles of the high dielectric permittivity ceramic filler in thepolymer material has a greater relative permittivity than the polymermaterial. In another and/or alternative non-limiting embodiment, thepolymer material has a greater breakdown strength than one or more ofthe particles of the high dielectric permittivity ceramic filler in thepolymer material. In another and/or alternative non-limiting embodiment,the polymer material has a greater breakdown strength than any of theparticles of the high dielectric permittivity ceramic filler in thepolymer material. In another and/or alternative non-limiting embodiment,the composite film has a dielectric constant of at least about 25% adielectric constant of any polymer in the polymer material, typically atleast about 100% a dielectric constant of any polymer in the polymermaterial, and more typically at least about 150% a dielectric constantof any polymer in the polymer material. In another and/or alternativenon-limiting embodiment, the high dielectric permittivity ceramic fillercomprises about 1 vol. % to 95 vol. % of the composite film (and allvalues and ranges therebetween). In another and/or alternativenon-limiting embodiment, the high dielectric permittivity ceramic fillercomprises about 5-25 vol. % of the composite film. The amount of highdielectric permittivity ceramic filler included in the composite film isgenerally selected so the high dielectric permittivity ceramic filler isbelow that percolation threshold of the composite film. In anotherand/or alternative non-limiting embodiment, the high dielectricpermittivity ceramic filler is calcined at a temperature of about 800°C. to about 1300° C. (and all values and ranges therebetween). Inanother and/or alternative non-limiting embodiment, the calcined highdielectric permittivity ceramic filler is post-heat treated. In anotherand/or alternative non-limiting embodiment, the post-heat treatingincludes one or more processes selected from the group consisting ofquench in water, quench in ice water, quench in liquid nitrogen, andheat above melting point. In another and/or alternative non-limitingembodiment, the post heat treating of the calcined high dielectricpermittivity ceramic filler is used to improve breakdown strength of thehigh dielectric permittivity ceramic filler and/or achieve higher energydensity of the high dielectric permittivity ceramic filler. In anotherand/or alternative non-limiting embodiment, the stretching or aligningof the composite film is used to achieve higher energy density of thecomposite film. In another and/or alternative non-limiting embodiment,the process of stretching or aligning includes one or more processesselected from the group consisting of uniaxial stretching and biaxialstretching. In another and/or alternative non-limiting embodiment, athickness of the composite film is at least about 1 μm. In anotherand/or alternative non-limiting embodiment, the thickness of thecomposite film is about 1 μm to 1 mm (and all values and rangestherebetween). In another and/or alternative non-limiting embodiment,the composite film is included in a device or component selected fromthe group consisting of power pulse devices, energy storage devices,inverters, converters, motors, DC bus capacitors, and high-powerlighting. In another and/or alternative non-limiting embodiment, thecomposite film is included in a device or component selected from thegroup consisting of radar devices, lasers, rail guns, high-powermicrowave devices, defibrillators, and pacemakers. In another and/oralternative non-limiting embodiment, there are provided power pulsedevices, energy storage devices, inverters, converters, motors, DC buscapacitors, or high-power lighting that includes a composite film of thepresent invention. In another and/or alternative non-limitingembodiment, the high dielectric permittivity ceramic filler has adielectric constant in bulk form of over 10,000 from a temperature rangeof room temperature (e.g., 20° C.−22° C.) to 100° C. In another and/oralternative non-limiting embodiment, the high dielectric permittivityceramic filler has a broad curie point range (e.g., a temperature rangeof at least about 10° C., and typically at least about 20° C.−200° C.).In another and/or alternative non-limiting embodiment, the compositefilm has a film energy storage density that exceeds 10 J/cc, andtypically exceeds 20 J/cc.

In one non-limiting object of the present invention, there is providedimproved nanocomposite films.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device for storing, and/orcontrolling, and/or manipulating a charge and/or electrical energyhaving a nanocomposite film as a dielectric layer.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a method to fabricate nanocompositefilms by incorporating a core-shell structure with high dielectricpermittivity nanoparticle into a high breakdown strength polymermaterial to create a gradient interface to improve breakdown strength,leading to high energy density.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a method to optimize the dielectricperformance of the nanocomposite film by adjusting the crystal structureof the filler, which method optionally includes doping a differentelement in the materials at different temperature; and/or which methodoptionally includes incorporating different structures of fillers in thepolymer material, the dielectric permittivity of the materials can betuned as well as the energy storage performance

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a dielectric layer that is a thinfilm or thick film.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device or method wherein anycomposite film comprises high dielectric permittivity ceramic fillers asthe core and high breakdown strength ceramic as the shell, and whereinthe core-shell ceramics can optionally be modified with differentfunctional group, which can optionally be bonded with polymer material.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device or method wherein theshell material can increase the breakdown strength of the core.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device or method wherein thefunctional groups bonded with the shell can improve the dispersion ofthe particles in the polymer as well as improve the breakdown strengthof the composite materials.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device or method wherein adielectric permittivity filler (>1000) is necessary for the compositecapacitor, and can optionally include one or more ferroelectricmaterials such as lead zirconate titanate (Pb(Zr_(x)Ti_(1-x))O₃),Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃ (PMN-PT), BaTiO₃ and so on, and/or anyother high dielectric materials, for example, calcium copper titanate(CaCu₃Ti₄O₁₂).

In another and/or alternative non-limiting object of the presentinvention, the nanocomposite has a dielectric constant that is largerthan the value of a dielectric constant of any of the powders used toform the nanocomposite, and is typically 1.1-100 times greater (and allvalues and ranges therebetween) than the of value of a dielectricconstant of any of the powders used to form said nanocomposite.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device or method wherein the highbreakdown strength shell materials include a thin layer of highbreakdown strength material such as ceramic (e.g., Al₂O₃, SiO₂, etc.),mica, diamond and others.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device or method wherein thethickness of the shell can range from 10 Å to 1 μm (and all values andranges therebetween).

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device or method wherein thefunctional groups bonded with the shell can include one or more groupsof amine group, hydroxyl group or others selected from phosphonategroup, a silyl group, or a carboxylic group and others.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device or method wherein themodified hierarchical particles are well dispersed in the polymersolution.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device or method wherein theparticles can be dispersed in the polymer solution.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device or method wherein ahigh-power mixing arrangement can be used to disperse the particles inthe solution, wherein such high-power mixing arrangement can include ahigh-power horn sonication, ultrasonic dispersion, etc.

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device or method wherein anyquench procedure can be used to improve the breakdown strength of thenanocomposites to achieve high-energy density, such as quenching inwater, quenching in ice water, and/or quenching in liquid gas (e.g.,nitrogen, etc.).

In another and/or alternative non-limiting object of the presentinvention, there is the provision of a device or method wherein anycontinuous setup to fabricate nanocomposites using the method can beused.

These and other objects, features and advantages of the presentinvention will become apparent in light of the following detaileddescription of preferred embodiments thereof, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the XRD patterns of doped BaTiO₃ calcined atdifferent temperatures showing that the crystal structures vary withcalcining temperature, wherein the top line is at the temperature 1200°C., the second line is at the temperature 1150° C., the third line is atthe temperature 1000° C., and the fourth and bottom line is at thetemperature 950° C.;

FIG. 2 illustrates the ability to control the dielectric constant of thenanocomposites by the incorporation of 7.5 vol % BaTiO₃ particles, whichare calcined at different temperatures;

FIG. 3 illustrates modified nanoparticles creating a gradient interfacebetween a filler and a polymer material to achieve high-energy densitynanocomposite;

FIG. 4 illustrates the hierarchical structure of (a) a TEM picture; and(b) a doped BaTiO₃ nanoparticle developed for ultra-high-energy densitynanocomposite capacitors;

FIG. 5 illustrates a Weibull distribution of the observed dielectricbreakdown strength of a dielectric nanocomposite film including dopednanoparticles with gradient interface; and,

FIG. 6 illustrates the energy density (19.6 J/cc) calculated fromtypical D-E loop of nanocomposites dielectric nanocomposite film (a);and red arrows illustrating how the nanocomposite films failed underhigh electric field (b).

DETAILED DESCRIPTION OF INVENTION

The present invention relates in general to high-energy densitynanocomposite capacitors that include nanoceramic filler in a polymermaterial. The invention also relates to a nanocomposite having a highdielectric permittivity nanoengineered particle dispersed into a highbreakdown strength polymer material to achieve high-energy density. Theinvention also related to nanocomposite films and a method for makingsuch films. The nanocomposite films are formed in the followingprocess: 1) create high dielectric permittivity ceramic fillers withcore-shell structure and 2) modify the surface with functional groups.The resulted engineered nanoparticles are dispersed into the polymermaterial; the mixture is then solution cast into the thin nanocompositefilms.

The dielectric permittivity of the nanocomposite can be improved byincorporating high dielectric permittivity fillers into a polymermaterial. The invention is directed to a method to prepare dopednanoceramic fillers calcined at different temperatures to tune thedielectric properties of the nanocomposites. The novel fabricationmethod is generally comprised of the steps of 1) ball mill the powder,and 2) calcine the powder at different temperatures. In the presentinvention, high-energy density nanocomposite capacitor films can bebased on the doped BaTiO₃ particles((Ba_(0.9575)Nd_(0.0025)Ca_(0.04))[Ti_(0.815)Mn_(0.0025)Y_(0.18)]_(0.997)O₃)that have a dielectric constant around 33,000 at room temperature whichis about ten times higher than conventional BaTiO₃ particles.

Doped barium titanate with the formulaBa_(0.9575)Nd_(0.0025)Ca_(0.04))[Ti_(0.815)Mn_(0.0025)Y_(0.18)]_(0.997)O₃was produced by ball milling BaCO₃, Nd₂O₃, CaCO₃, TiO₂, MnCO₃, and Y₂O₃for 24 hours. The mixed powder was then calcined at high temperature,such as 800° C. to 1300° C. (and all values therebetween). It isobserved that different temperature calcining yields different crystalstructure and particle size of doped materials. In this non-limitingcomposition, the nanocomposites with doped BaTiO₃ nanoparticles calcinedat 900° C. have the highest dielectric permittivity. Other similarcompositions will have a different optimum calcining temperature.

While this non-limiting example was directed to BaTiO₃, it is understoodthat other high dielectric materials can be chosen, doped, coated andactivated for the same purpose. These materials include any selectedferroelectric materials such as lead zirconate titanate(Pb(Zr_(x)Ti_(1-x))O₃), Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃ (PMN-PT), BaTiO₃and so on, or any other high dielectric materials, for example, calciumcopper titanate (CaCu₃Ti₄O₁₂). As defined herein, a high dielectricmaterial has a dielectric constant (i.e., relative permittivity) at thefrequency of 1 kHz at room temperature (e.g., 70° F.) of at least 100,typically at least 300, and more typically at least 500 (e.g.,100-100,000 and all values and ranges therebetween).

Assuming there is no loss, the energy density of the capacitor can beexpressed by the following equation: U=κE²/2, where U is energy density,κ is the dielectric permittivity and E is the dielectric breakdownstrength. The energy density is a square relationship to the breakdownstrength, while it is linear to the dielectric permittivity of thenanocomposite. However, while current nanocomposites improve thedielectric permittivity of the capacitor, the gains come at the expenseof the breakdown strength, which limits the ultimate performance. One ofthe main reasons of this limitation is that these high dielectricpermittivity fillers have low breakdown strength resulting in alow-energy density capacitor.

The invention is directed to improving the breakdown strength of thenanocomposite by creating gradient interfaces between the polymermaterial and the filler. First, the core-shell structure dielectricparticle is designed. The shell materials typically have high dielectricpermittivity, and the core materials are chosen from many that haveexceptional high voltage breakdown (particularly in thin films) such asAl₂O₃, SiO₂, mica, diamond and so on. This core-shell structure not onlyprovides high dielectric permittivity, but also improves the breakdownstrength of the shell. Also, the shell structure can improve the highcharge storage capability at the dielectric-dielectric interfaces. Thethickness of the shell can range from 10 Å to 500 nm, and in some casesfrom 5 Å to 1000 nm (and all values therebetween).

Following the encapsulation, hierarchical particles are functionalizedwith different terminated groups to create the gradient interfacebetween the polymer material and the filler. The gradient functionalgroup not only improves the compatibility of the filler with the polymermaterial, but also improves the breakdowns strength of thenanocomposite. The terminated group can be any group to create the bondbetween the polymer material and filler, such as, but not limited to,amine group, hydroxyl group or others selected from phosphonate group, asilyl group, or a carboxylic group and others. The process for coatingthe one or more functional groups on the outer surface of the shell isnon-limiting. Generally the thickness of the coating or layer of the oneor more functional groups on the outer surface of the shell is about 1 Åto 200 nm.

By incorporating these hierarchical particles into a polymer material,the invention provides a novel method to prepare a high-energy densitynanocomposite capacitor. The polymers can be selected from manydielectric films including polyvinylidene fluoride (PVDF), PVDFcopolymers such as trifluoroethylene (P(VDF-TrFE)), hexafluoropropylene(P(VDF-HFP)) and chlorotrifluoroethylene (P(VDF-CTFE)) as well asterpolymers such as poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)),polytetrafluoroethylene (PTFE), polyimide (PI), Teflon™, polyethylenenaphthalate (PEN), polypropylene (PP), polycarbonate (PC), polystyrene(PS), polyphenylene sulfide (PPS), polyether ether ketone (PEEK),polyethylenimine (PEI), polyarylsulfones (PSU), and others. Thenanofillers can be dispersed into the polymer solution; thenanocomposite films can then be solution cast into films. It isunderstood by one skilled in the art that these films can be made byextrusion, blown film techniques, calendaring and other film preparationtechniques. The films can then be heat treated to reach high breakdownstrength and high dielectric permittivity to reach high-energy density.

The following example is directed to tape casting technology thatprovides a means for producing large quantities of thin film materialsat a low cost. The system is easily scalable and ideal for processingmaterial for capacitors, which require high-quantity, low-costproduction.

Examples

Doped barium titanate with the formulaBa_(0.9575)Nd_(0.0025)Ca_(0.04))[Ti_(0.815)Mn_(0.0025)Y_(0.18)]_(0.997)O₃was produced by ball milling BaCO₃, Nd₂O₃, CaCO₃, TiO₂, MnCO₃, and Y₂O₃for 24 hours. Different calcining temperatures will yield differentfinal structures of the powder, thereby leading to a change in thedielectric properties of the materials. FIG. 1 illustrates the XRDpatterns of the samples calcined at different temperatures (900° C.,1000° C., 1050° C., and 1200° C.). As illustrated in FIG. 1, peakscorresponding to BaTiO₃ as well as peaks corresponding to other dopedceramic phases are illustrated. The peaks around 25 and 63 degreessuggest that there was some phase change after 1050° C. during thecalcining process. This phase change was likely brought on by dopingwith many differently sized elements (Ca, Mn, Y and Nd). As illustratedin FIG. 1, there is a slightly different final structure for dopedBaTiO₃ that was calcined at different temperatures.

The temperatures (950° C., 1000° C., 1150° C. and 1200° C.) were used toillustrate the effect of the BaTiO₃ particles calcined at differenttemperatures on the dielectric and energy storage properties of thenanocomposites. FIG. 2 is a graph illustrating the dielectric constantof the nanocomposites with the incorporation of 7.5 vol % BaTiO₃ ceramicfillers, which are calcined at different temperatures (950° C., 1000°C., 1150° C. and 1200° C.). It is showed that the dielectric constant ofthe nanocomposite is influenced by the filler nanoparticles, which arecalcined at different temperatures. By adjusting the structure andparticle of the ceramic fillers in the polymer material, the dielectricconstant of the composites can be tuned.

FIG. 3 schematically illustrates the hierarchical structure of ceramicfillers in the polymer material to create a high-energy densitynanocomposite capacitor. More specially, high dielectric permittivityceramic filler is designed as a core-shell structure. The core has ahigh dielectric permittivity, while the shell materials have highbreakdown strength. In a representative example, particle cores occupyat least about 50% (e.g., 50-99% vol. % and all values and rangestherebetween) of the total of the volume in core-shell ceramic fillers;however, this is not required. Representative materials that can be usedto form the core-shell structure can be any high dielectric permittivitymaterials (e.g., barium titanate, lead zirconium titanate, CCTO, etc.).The shell is a thin film with high breakdown strength materials toprotect the high dielectric core structure. Representative materials canbe any high-breakdown strength materials (e.g., Al₂O₃, SiO₂, mica,diamond and others). The particle cores can have a variety of shapes(e.g., spherical, elongated, or irregular), and a variety of sizes. Theparticle cores have a relatively small size, usually less than about 100μm (e.g., 0.05-500 μm and all values and ranges therebetween), and thethickness of the film is generally between about 0.1 nm to 1 μm (and allvalues and ranges therebewteen).

FIG. 4 illustrates an example to create a gradient interface between thefiller and polymer material, as well as a core-shell structurenanoparticle. The nano-engineered particle designed for thenano-laminated dielectric particle is illustrated in FIG. 4a . In thisnon-limiting example, high dielectric permittivity doped BaTiO₃nanoparticles with around 100 nm were chosen as core materials. Thecoating materials have exceptional high voltage breakdown (particularlyin thin films), as well as providing for high-charge storage at thedielectric-dielectric interfaces. The sol-gel process uses an ultrasonichorn to disperse BaTiO₃ in anhydrous ethanol, a solution of aluminumisopropoxide in anhydrous ethanol was then added to the BaTiO₃dispersion, and was again blended ultrasonically to fully disperse andcoat the particles. This step was followed by the addition of deionizedwater to the mixture. The aluminum isopropoxide, which clings to thesurface of the BaTiO₃, undergoes a hydrolysis reaction and leavesaluminum oxide on the surface of the particles. The particles were thendried in air and calcined to densify the Al₂O₃ surface coating. Thismethod successfully coated the doped barium titanate with 10 nm Al₂O₃film observed in high-resolution transmission electron microscopy(HRTEM), as shown on the FIG. 4 b.

In order to prepare high-energy nanocomposite films, these nanoparticlescan be dispersed in the dimethylformamide (DMF)/polyvinylidene fluoride(PVDF) solution by high-power horn solicitation. The entire processdeveloped by this invention (encapsulation, surface function, high-powerhorn dispersion) stabilizes the particles in the solution for about oneweek, and sometimes more. Nanocomposite films were cast by using asolution casting method. The breakdown strength was measured by using anelectrostatic pull-down method with Weibull distribution analysis asshown in FIG. 5. Pull-down between the conductive substrate and a brassdome typically occurs at an electrical field of 10 MV/m and ismaintained until breakdown occurs over the test area. The pull-downmethod was chosen over a point-contact method to avoid any mechanicalforce that might cause premature breakdown at the contact point.Breakdown testing was performed in silicon oil to avoid electric arcingand was performed using a high voltage supply by sweeping the appliedvoltage until sample failure, as evidenced by spurious current changes.Every sample was tested for at least 15 data points. Dielectricbreakdown strength was then extracted from a fit using Weibull failurestatistics across at least 15 tests per sample. Following the proceduredeveloped in this invention, the dielectric strength of thenanocomposites can reach 442 MV/m. It should be noticed that thebreakdown strength of the nanocomposites reported here is much higherthan that of any composites reported in current literature.

Energy density is identified through the measurement of the dischargeenergy from the sample when subjected to a unipolar electric field. Theelectric displacement-electric field (D-E) loops of the capacitor weremeasured using a Sawyer-Tower circuit, which allowed for the directcomputation of the energy density U=∫EdD (illustrated in FIG. 6a ). Thepolarization loop was measured with increasing electric field untilbreakdown occurred and the maximum energy could be recorded. The graphon the left side of FIG. 6 shows the typical D-E loops of thenanocomposite films. From the graph, it can be calculated that thenanocomposite film can achieve an energy density 19.6 J/cc. FIG. 6b alsodemonstrates the self-healing ability of the metalized nanocompositefilm. Under a high electric field, the current vaporizes the thinelectrodes on the films in the immediate vicinity of the current flow(red arrow). This means that the local breakdown of the filmnanocomposite will not influence the work status of the capacitor, andwill help to greatly extend the life of the capacitor and the equipmentin which it is installed.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained, andsince certain changes may be made in the constructions set forth withoutdeparting from the spirit and scope of the invention, it is intendedthat all matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense. The invention has been described with reference topreferred and alternate embodiments. Modifications and alterations willbecome apparent to those skilled in the art upon reading andunderstanding the detailed discussion of the invention provided herein.This invention is intended to include all such modifications andalterations insofar as they come within the scope of the presentinvention. It is also to be understood that the following claims areintended to cover all of the generic and specific features of theinvention herein described and all statements of the scope of theinvention, which, as a matter of language, might be said to fall therebetween. The invention has been described with reference to thepreferred embodiments. These and other modifications of the preferredembodiments as well as other embodiments of the invention will beobvious from the disclosure herein, whereby the foregoing descriptivematter is to be interpreted merely as illustrative of the invention andnot as a limitation. It is intended to include all such modificationsand alterations insofar as they come within the scope of the appendedclaims.

1. A method for forming a composite film comprising: a. forming aplurality of particles of high dielectric permittivity ceramic filler,said high dielectric permittivity ceramic filler having a core-shellstructure, a core of said core-shell structure having a differentcomposition than a shell of said core-shell structure, said shell heatedafter being coated on said core; b. dispersing a plurality of saidparticles of said high dielectric permittivity ceramic filler havingsaid one or more functional groups into a polymer material; and, c.solution casting said polymer material having said plurality of saidcoated particles of said high dielectric permittivity ceramic fillerinto a film to form said composite film.
 2. The method as defined inclaim 1, wherein said polymer material includes polar groups.
 3. Themethod as defined in claim 1, wherein said shell is a dielectricmaterial that has a breakdown strength that is at least three times thatof said material used to form said core.
 4. The method as defined inclaim 1, wherein said particles of said high dielectric permittivityceramic filler have a particle size of less than 1 micron.
 5. The methodas defined in claim 1, wherein said particles of said high dielectricpermittivity ceramic filler have a particle size of about 10 nanometerto less than about 1 μm.
 6. The method as defined in claim 1, whereinsaid particles of said high dielectric permittivity ceramic filler havea particle size of about 50-450 nanometers.
 7. The method as defined inclaim 1, wherein said particles of said high dielectric permittivityceramic filler have a particle size of less than about 200 nanometers.8. The method as defined in claim 1, wherein said shell has a coatingthickness of at least about 10 Å and less than 1 μm.
 9. The method asdefined in claim 1, wherein said shell has a coating thickness of lessthan 20 nanometer.
 10. The method as defined in claim 1, wherein saidcore of said high dielectric permittivity ceramic filler includes a highdielectric material, said shell includes a high breakdown strengthmaterial, said core is at least partially encapsulated by said shell.11. The method as defined in claim 8, wherein said high dielectricmaterial includes one or more materials selected from the groupconsisting of BaTiO₃, (Pb(Zr_(x)Ti_(1-x))O₃),Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃, CaCu₃Ti₄O₁₂, TiO₂, BaSrTiO₃, andBa_(0.8)Pb_(0.2)(Zr_(0.12)Ti_(0.88))O₃.
 12. The method as defined inclaim 1, wherein said shell includes one or more materials selected fromthe group consisting of Al₂O₃, SiO₂, Si₃N₄, MgO, aluminosilicates, mica,and diamond.
 13. The method as defined in claim 1, wherein said highdielectric material includes doped BaTiO₃ and said shell includes one ormore compounds selected form the group consisting of Al₂O₃, MgO andSiO₂.
 14. The method as defined in claim 1, wherein said thickness ofsaid shell is less than said particle size of said core.
 15. The methodas defined in claim 1, wherein said composite film has a greaterdielectric constant than a dielectric constant of said polymer materialand any polymer included in said polymer material that is used to formsaid composite film, said composite film has a greater breakdownstrength than a breakdown strength of any of said high dielectricpermittivity ceramic filler in said composite film.
 16. The method asdefined in claim 1, wherein said high dielectric permittivity ceramicfiller in said composite film has one or more properties selected fromthe group consisting of a) a plurality of different particle sizes ofsaid high dielectric permittivity ceramic filler, b) said highdielectric permittivity ceramic filler formed of particles that havebeen calcined at different temperatures, and/or c) said high dielectricpermittivity ceramic filler formed of particles formed of differentmaterials.
 17. The method as defined in claim 1, wherein a dielectricperformance, dielectric permeability, energy storage performance, andcombinations thereof of said composite film is achieved by adjusting acrystal structure, a particle size, or combinations thereof of said highdielectric permittivity ceramic filler, said adjusting of said crystalstructure, a particle size, or combinations thereof is achieved by a)calcining a plurality of said high dielectric permittivity ceramicfiller at different temperatures for inclusion in said polymer material,b) incorporating different composition high dielectric permittivityceramic filler in said polymer material, c) incorporating a plurality ofdifferent particle sizes of said high dielectric permittivity ceramicfiller in said polymer material, and any combination of a), b), and c).18. The method as defined in claim 1, wherein said polymer materialincludes one or more compounds selected from the group consisting ofpolyvinylidene fluoride (PVDF), PVDF copolymers such astrifluoroethylene (P(VDF-TrFE)), hexafluoropropylene (P(VDF-HFP)) andchlorotrifluoroethylene (P(VDF-CTFE)) as well as terpolymers such aspoly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)(P(VDF-TrFE-CFE)), polytetrafluoroethylene (PTFE), polyimide (PI),Teflon™, polyethylene naphthalate (PEN), polypropylene (PP),polycarbonate (PC), polystyrene (PS), polyphenylene sulfide (PPS),polyether ether ketone (PEEK), polyethylenimine (PEI), andpolyarylsulfones (PSU).
 19. The method as defined in claim 1, includingthe step of applying one or more functional groups to an outer surfaceof said particles of said high dielectric permittivity ceramic filler,said one or more functional groups includes one or more compoundsselected from the group consisting of an amine group, a hydroxyl group,a phosphonate group, a silyl group, and a carboxylic group.
 20. Themethod as defined in claim 1, wherein one or more of said particles ofsaid high dielectric permittivity ceramic filler in said polymermaterial has a greater relative permittivity than said polymer material.21. The method as defined in claim 1, wherein all of said particles ofsaid high dielectric permittivity ceramic filler in said polymermaterial has a greater relative permittivity than said polymer material.22. The method as defined in claim 1, wherein said polymer material hasa greater breakdown strength than one or more of said particles of saidhigh dielectric permittivity ceramic filler in said polymer material.23. The method as defined in claim 1, wherein said polymer material hasa greater breakdown strength than any of said particles of said highdielectric permittivity ceramic filler in said polymer material.
 24. Themethod as defined in claim 1, wherein said composite film has adielectric constant of at least 150% a dielectric constant of anypolymer in said polymer material.
 25. The method as defined in claim 1,wherein said high dielectric permittivity ceramic filler comprises about1 vol. % to 95 vol. % of said composite film.
 26. The method as definedin claim 1, wherein said high dielectric permittivity ceramic fillercomprises about 5-25 vol. % of said composite film.
 27. The method asdefined in claim 1, wherein said core of said high dielectricpermittivity ceramic filler is calcined at a temperature of about 800°C. to about 1300° C. prior to applying said shell to said core.
 28. Themethod as defined in claim 1, including the step of post-heat treatingsaid calcined core, said step of post-heat treating includes one or moreprocesses selected from the group consisting of quench in water, quenchin ice water, quench in liquid nitrogen, and heat above melting point.29. The method as defined in claim 1, wherein said step of post-heattreating said calcined core is used to improve breakdown strength ofsaid high dielectric permittivity ceramic filler, achieve higher energydensity of said high dielectric permittivity ceramic filler, orcombinations thereof.
 30. The method as defined in claim 1, includingthe step of stretching or aligning said composite film to achieve higherenergy density of said composite film, said step of stretching oraligning includes one or more processes selected from the groupconsisting of uniaxial stretching, and biaxial stretching.
 31. Themethod as defined in claim 1, wherein a thickness of said composite filmis at least about 1 μm.
 32. The method as defined in claim 1, wherein athickness of said composite film is about 1 μm to 1 mm.
 33. The methodas defined in claim 1, wherein said composite film is included in adevice or component selected from the group consisting of power pulsedevices, energy storage devices, inverters, converters, motors, DC buscapacitors, and high-power lighting.
 34. The method as defined in claim1, wherein said composite film is included in a device or componentselected from the group consisting of radar devices, lasers, rail guns,high-power microwave devices, defibrillators, and pacemakers.
 35. Acomposite film formed by the method as defined in claim
 1. 36. A powerpulse device, an energy storage device, inverter, converter, motor, DCbus capacitor, or high-power lighting that includes a composite filmformed by the method as defined in claim
 1. 37. A composite filmcomprising a polymer material that includes a plurality of particles ofhigh dielectric permittivity ceramic filler, said high dielectricpermittivity ceramic filler having a core-shell structure, a core ofsaid core-shell structure having a different composition than a shell ofsaid core-shell structure.
 38. A high-power density dielectriccomposite, said composite includes: a high dielectric strength polymermaterial which can include polar groups; a surface functionalizedcore-shell high dielectric permittivity ceramic filler having an averageparticle size between 10 nm and 500 nm, said high dielectricpermittivity ceramic filler having a surface-functionalized core-shellstructure, containing a core of said core-shell structure having adifferent composition than a shell of said core-shell structure, wheresaid shell is formed of a dielectric material having a dielectricbreakdown strength of at least three times a breakdown strength of saidmaterial forming said core; and wherein said high dielectricpermittivity ceramic filler constitutes greater than 3 vol. % and lessthan 25 vol. % of said composite and a content of said high dielectricpermittivity ceramic filler in said composite does not reach apercolation threshold in said composite film.
 39. The high-power densitycomposite as defined in claim 38, wherein said high dielectricpermittivity ceramic filler has a dielectric constant in bulk form ofgreater than 10,000 over a temperature range of at least roomtemperature to 100° C.
 40. The high-power density composite as definedin claim 38, wherein said high dielectric permittivity ceramic fillerhas a broad curie point range.
 41. The high dielectric composite as inclaim 38, wherein the dielectric filler has an average particle sizebetween 30 and 80 nm.
 42. The high-power density composite as defined inclaim 38, wherein said composite film has a film energy storage densitythat is greater than 10 J/cc.
 43. The high-power density composite asdefined in claim 38, wherein said composite film has a film energystorage density that is greater than 20 J/cc.
 44. The high-power densitycomposite as defined in claim 38, wherein said high dielectric ceramicfiller includes one or more materials selected from the group consistingof doped BaTiO₃, (Pb(Zr_(x)Ti_(1-x))O₃), Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃,CaCu₃Ti₄O₁₂, TiO₂, BaSrTiO₃, and Ba_(0.8)Pb_(0.2)(Zr_(0.12)Ti_(0.88))O₃,and wherein said material can be heat treated at a temperature toachieve optimum performance.
 45. The high-power density composite asdefined in claim 38, wherein said polymer material includes one or morecompounds selected from the group consisting of polyvinylidene fluoride(PVDF), PVDF copolymers such as trifluoroethylene (P(VDF-TrFE)),hexafluoropropylene (P(VDF-HFP)) and chlorotrifluoroethylene(P(VDF-CTFE)) as well as terpolymers such as poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)),polytetrafluoroethylene (PTFE), polyimide (PI), Teflon™, polyethylenenaphthalate (PEN), polypropylene (PP), polycarbonate (PC), polystyrene(PS), polyphenylene sulfide (PPS), polyether ether ketone (PEEK),polyethylenimine (PEI), and polyarylsulfones (PSU).
 46. The high-powerdensity composite as defined in claim 38, wherein said shell has acoating thickness of at least about 10 Å and less than 100 nm.
 47. Thehigh-power density composite as defined in claim 38, wherein said shellhas an average coating thickness between 3 and 15 nanometers.
 48. Thehigh-power density composite as in claim 47, wherein the shell isproduced using a process selected from chemical vapor deposition, atomiclayer deposition, sol-gel coating, or solution coating.
 49. Thehigh-power density composite as defined in claim 38, wherein said highdielectric material includes one or more materials selected from thegroup consisting of doped BaTiO₃, (Pb(Zr_(x)Ti_(1-x))O₃),Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃, CaCu₃Ti₄O₁₂, TiO₂, BaSrTiO₃, andBa_(0.8)Pb_(0.2)(Zr_(0.12)Ti_(0.88))O₃.
 50. The high-power densitycomposite as defined in claim 38, wherein said shell includes one ormore materials selected from the group consisting of Al₂O₃, SiO₂, Si₃N₄,MgO, aluminosilicates, mica, and diamond.
 51. The high-power densitycomposite as defined in claim 38, wherein a coating thickness of saidcoating on said outer surface of said high dielectric permittivityceramic filler is about 3 Å to 80 nm.
 52. The high-power densitycomposite as defined in claim 38, wherein an said outer surface of saidhigh dielectric permittivity ceramic filler includes one or morefunctional groups on said outer surface of said high dielectricpermittivity ceramic filler, said functional groups include one or moregroups selected from an amine group, a hydroxyl group, a phosphonategroup, a silyl group, and a carboxylic group.
 53. The high-power densitycomposite as defined in claim 38, wherein said composite furtherincludes an additional dielectric insulator particles, said additionaldielectric insulator particles have a size of less than 150 nm, saidadditional dielectric insulator particles include one or more materialsselected from the group consisting of MgO, Al₂O₃, SiO₂ and otherinsulators.
 54. The high-power density composite as defined in claim 53,wherein said additional dielectric insulator particles have a surfacefunctionalization, which surface functionalization can primarily includean organosilane.
 55. The high-power density composite as defined inclaim 53, wherein said additional dielectric insulator particles have aparticle size of less 50 nm, and typically less than 20 nm.
 56. Thehigh-power density composite as defined in claim 53, wherein saidadditional dielectric insulator particles constitute about have a 0.2vol. % to 2 vol. % of said composite film.
 57. The high-power densityfilm composite as defined in claim 38, wherein said composite has adielectric constant that is at least 150% of a value of a dielectricconstant of said polymer material, and typically said composite has adielectric constant that is at least 200% of a value of a dielectricconstant of said polymer material.
 58. The high-power density compositeas defined in claim 38, wherein said composite has a breakdown strengththat is at least 80% of the breakdown strength of said polymer material,and typically said composite breakdown strength that is at least 90% ofthe breakdown strength of said polymer material.
 59. The high-powerdensity composite as defined in claim 38, wherein a concentration ofsaid high dielectric ceramic filler in said composite is different at anouter surface region of said composite than compared to an averageconcentration of said high dielectric ceramic filler in said composite.60. The high-power density composite as defined in claim 38, whereinsaid concentration of said high dielectric ceramic filler in saidcomposite is less at an outer surface region of said composite thancompared to an average concentration of said high dielectric ceramicfiller in said composite.
 61. The high-power density composite asdefined in claim 38, wherein said core is calcined at a temperature tooptimize or tune a structure, a particle size, or combinations thereofof said core.
 62. The high-power density composite as defined in claim61, wherein said core is calcined in a controlled atmosphere such as inoxygen partial pressure.
 63. The high-power density composite as definedin claim 38, wherein said composite is in the form of a film.
 64. Thehigh-power density film as defined in claim 61, wherein a thickness ofsaid composite film is 2-200 microns, said thickness of said film beingdesigned to allow operating at 30-60% of the effective film breakdownstrength at a selected operating voltage.
 65. The composite film as inclaim 37 in the form of printed layers, such as those used for passivedevices.